1. Field of the Invention
This invention relates to extraction of geothermal heat energy from the earth and more particularly to the stimulation of flow from geothermal wells and systems for recovering the heat carried by a carrier fluid, such as water, from geothermal wells.
It is known that the interior of the earth is a molten mass of rocks and is very hot. This geothermal heat energy may advantageously and efficiently be employed as a primary source of energy for the generation of power through fluid as a carrier. The fluid may be steam released from volcanic areas or hot water which is present in volcanic and in deep alluvial deposits that are porous enough to permit percolation of water to the deep hot zones. This water may have a temperature as high as 700.degree. F. at a depth of 5,000 feet.
Additionally, the carrier fluid may be injected into the earth by means of a well where the carrier fluid is vaporized upon contact with the heat energy in the earth. This heat energy may be present in dry rock beds or in fluids, such as water, in the well.
2. Description of the Prior Art
In some areas the heat energy within the earth is carried to the surface by steam. This steam may be used directly in turbines to drive the generator to generate electricity as the means of efficiently and effectively recovering the heat energy. Where there is a mixture of steam, noncondensibles, such as carbon dioxide, and hot water, the steam and noncondensibles may be separated in a flash chamber and then used in a steam turbine. The fluid from a geothermal well may flow naturally to the surface or may have to be pumped to the surface. Where pumping is required, it is typically accomplished by locating the pump at a selected level below the surface of the earth. When the pump is located in the well, a long drive shaft is generally required between the pump and the drive motor. These pumps and motors are relatively expensive and often require servicing which is also relatively expensive.
Other geothermal well pumping devices have been proposed, including an electrically driven pump where the motor and the pump are submersed in the well. This proposal has not been reduced to practice, and the relative cost and efficiency has not been determined. Many self-flowing water dominated wells do not spontaneously flow without some startup boosting. In the past, well start-up stimulation was accomplished mainly by one of the following three methods:
a. By pumping fresh water down the well; PA1 b. By inserting a tube down the well and pumping air or inert gases down the tube; PA1 c. By inserting a tube down the well and pumping liquefied gases, such as liquid nitrogen or carbon dioxide, down the tube.
In each case, the principle of the well stimulation is the same, namely, a reduction in the density of the well fluid present in the well casing to cause disequilibrium in the well hydraulic system, and thus, commence the flow. Once started, the self-flowing well will continue to flow without any additional stimulation.